Piezoelectric vibrators are widely used as oscillators or band-pass filters. As a conventional piezoelectric vibrator, for example, Japanese Unexamined Patent Application Publication No. 2014-197615 describes a surface-mount crystal unit having a structure that hermetically seals off a crystal element from the outside air. The surface-mount crystal unit described in this document includes a substrate having the crystal element mounted thereon, and a lid configured to hermetically seal the crystal element by means of an adhesive (see, paragraph [0002] in Japanese Unexamined Patent Application Publication No. 2014-197615).